The present invention relates to a method of magnetizing a permanent magnet motor.
An electric motor for driving a refrigerating cycle oriented compressor involves the use of a permanent magnet motor 10 constructed of, as shown in FIG. 11, a stator 13 including U-phase stator windings 12Ua, 12Ub wound in multi-layers on, for example, six pieces of pole teeth 11, V-phase stator windings 12Va, 12Vb wound thereon and W-phase stator windings 12Wa, 12Wb wound thereon, and a rotor 15 including four pieces of permanent magnets 14 disposed at an angle of 90xc2x0 in a peripheral direction inwardly of the stator 13.
The permanent magnet 14 is constructed by incorporating the stator 13 and the rotor 15 and thereafter magnetizing unmagnetized magnet materials provided in four circular arc holes 16 of the rotor 15 by flowing a large direct current through the stator windings.
For attaining this magnetization, as illustrated in FIG. 12, a DC power source 17 applies a DC voltage to between two arbitrary-phase winding terminals, e.g., a U-phase winding terminal 12U and a V-phase winding terminal 12V, and the direct current flows through the U-phase stator windings 12Ua, 12Ub and the V-phase stator windings 12Va, 12Vb. With this DC excitation, magnetic fluxes occur in the motor 10 as indicated by arrowheads in FIG. 13. Forces F attracting each other are produced in the windings through which the direct currents flow in the same direction as produced in the two adjacent-phase windings 12Ua, 12Va or the windings 12Ub, 12Vb by dint of interaction between those magnetic fluxes and the currents flowing through the windings, with the result that those windings 12Ua, 12Va, 12Ub, 12Vb might be deformed as illustrated in FIG. 14.
If quantities of these deformations are large, the windings of the phases different from each other come into contact with each other, thereby causing a dielectric breakdown. Besides, a large force is applied to a corner 19a of an insulating bobbin 19 wound with the windings and to a proximal portion of a flange, and these portions are flawed. Therefore, those stator windings 12Ua, 12Ub, etc. might undergo a ground fault.
It is a primary object of the present invention to provide a method of magnetizing a permanent magnet motor, which is capable of preventing stator windings, an insulating bobbin, etc. from being damaged when forming a permanent magnet by magnetizing an unmagnetized magnet material.
To accomplish the above object, according to one aspect of the present invention, a method of magnetizing a permanent magnet motor comprises a step of preparing an incomplete permanent magnet motor, which is constructed of a stator having stator windings wound in multi-layers on a plurality of magnetic pole teeth of a stator core respectively through an insulating bobbin, and a rotor including unmagnetized magnet material disposed in a rotor core, a step of inserting a spacer in a gap in a slot between the two stator windings wound on the adjacent magnetic teeth, a step of magnetizing the magnet material by electrifying the stator windings with a direct current in a state of the spacer being inserted therebetween, a step of removing the spacer after finishing the step of magnetizing, and thus forming a permanent magnet.
By removing the spacer, space substantially corresponding to the thickness of the spacer is formed between the windings so that the windings are effectively cooled. Further, when the motor according to the present invention is applied to an enclosed compressor, it is possible to flow the emitted coolant from the compressor through the space, thereby the motor windings are effectively cooled and to effectively separate the coolant from the lubricant.
According to the present invention, when magnetizing the unmagnetized magnet material, the stator windings and the insulating bobbin are prevented from being damaged, and it is also feasible to prevent a ground fault and a short-circuit fault of the stator windings.
The spacer may be inserted in between a pair of windings through which at least an electric current flows in the same direction among pairs of windings of adjacent slots.
A required sufficient peripheral thickness of the spacer may be on the order of 70%-110% of the gap between the stator windings.